FR3029353A1 - BACKLIGHT DEVICE, IN PARTICULAR FOR HIGH HEAD DISPLAY AND HIGH HEAD DISPLAY FOR MOTOR VEHICLE - Google Patents

Abstract

The invention relates to a backlighting device (14), in particular for a head-up display comprising at least one light-emitting diode (16) emitting light beams, an optical beam (20) for shaping the light beams, a light diffuser (22) receiving the shaped light beams characterized in that it further comprises a heat sink (18) made of at least two parts comprising on the one hand a base plate (50) and on the other hand at least one strip (52) fixed on said base plate, the strip including at least one fold (90) to form at least one cooling fin (80) and at least one zone (60) for coming into thermal contact with said base plate (50).

Description

BACKGROUND OF THE INVENTION Technical Field of the Invention The invention relates to a backlighting device, in particular for head-up displays for a motor vehicle. BACKGROUND OF THE DISCLOSURE BACKGROUND OF THE INVENTION The invention will find its applications, for example, in motor vehicles to inform users of the vehicle, in particular its driver. It is known to equip a motor vehicle with a head-up display, also known as head-up display or HUD (for "headup display" in English). Such a display is placed in the field of vision of the driver and displays information relating to the state of the vehicle, traffic or other.

This type of head-up display for a motor vehicle requires obtaining an image with sufficient brightness so that the user, and in particular the driver of the vehicle, can sufficiently see the image, and this in any situation, day and night and weather conditions (sunny or cloudy).

Among the possible technologies for forming such an image by means of the head-up display, the most used in the prior art is the liquid crystal screen technology, in particular thin-film transistors, called TFT-LCDs. LCD (for Thin-Film Transistor Liquid Crystal Display). These TFT-LCD screens require, for the display of an image, a backlight usually made by a plurality of light-emitting diodes (LED or LED for Light-Emitting Diode). In practice, this TFT-LCD screen and the backlight are included in a set called image generation device also called "imager".

Nevertheless, because of their operation based on polarized light, these TFT-LCD screens have the disadvantage of significantly reducing the light power from the backlight: with the use of a conventional TFT-LCD screen, it is estimated that the transmission rate of the screen is about 5% of the light power of the backlight. This low value is due in particular to the first polarizer present in the screen which allows only the light corresponding to a certain polarization, whereas the LEDs produce light with several polarizations: all the polarizations do not correspond to that which passes through the polarizer are then lost.

Therefore, for the display of an image by the display with a sufficient luminous power, it is necessary to use a backlight of a significant luminous power since the displayed image will have a light power of the order of 5% of this backlighting power. This generates significant energy consumption, as well as significant losses in the form of heat, which in addition can degrade the components and therefore require the use of bulky heat sinks. OBJECTS OF THE INVENTION The invention aims to overcome at least some of the above disadvantages. In particular, the invention aims to provide a backlight device with good optical performance while providing a small footprint. DESCRIPTION OF THE INVENTION To this end, the subject of the invention is a backlighting device, in particular for a head-up display comprising: at least one light emitting diode emitting light beams; optical beam shaping; light, - a light diffuser receiving the shaped light beams characterized in that it further comprises a heat sink made of at least two parts comprising on the one hand, a base plate and on the other hand at least one strip attached to said base plate, the strip having at least one ply to form at least one cooling fin and at least one zone intended to come into thermal contact with said base plate. Fines made of folded sheet, also called folded strip, has a better thermal efficiency than fins resulting from molding. Because the heat generated by the diodes is efficiently discharged by the two-part heat sink, the shaping optics can be placed closer to the diodes, especially at about 0.5mm. Thus, the height and size of the backlighting device can be reduced, resulting in a smaller footprint of a head-up display (HUD) as a whole. This last point is very important at the level of the dashboard where the display will be integrated and where every millimeter of gain in size is very important. In addition, the optical efficiency of the device can be increased by placing the shaping optics closer, as side losses of the cone of light are reduced. . Thanks to the invention, it is thus possible to provide a head-up display device intended to be arranged in a small footprint without degrading the optical performance. The backlighting device may further comprise one or more of the following characteristics taken alone or in combination: the strip comprises several plies and several zones in contact with the base plate. - the strip has a form of crenellations. thermal paste is interposed between the base plate and at least one contact zone of the strip. the strip is fixed on the base plate by welding, screwing or crimping. the strip and / or the base plate are made of aluminum. the strip is disposed on a lower face of the base plate opposite to an upper face of the base plate carrying the light-emitting diodes. - The base plate of the heat sink has on its side opposite to that carrying the light emitting diodes grooves housing the fins. The grooves have a curved or flat cross-section and the contact areas of the cooling fins are in the form of a folded strip, the fold returns being fixed in curved or flat cross-sectional grooves. - the strip is at the right of the light emitting diodes. - The strip is offset from the location of the light emitting diodes and disposed on an extension of the base plate. the extension of the base plate has a different orientation of the part of the base plate located at the right of the light emitting diodes. - The base plate comprises a fold so that the extension of the base plate may have a different orientation of the portion of the base plate located at the right of the light emitting diodes. the shaping optics comprises a lens array, each lens being placed in front of a light-emitting diode and forming a collimator. The invention also relates to an image generation device, in particular for head-up display, comprising a liquid crystal screen and a backlighting device of this liquid crystal screen as defined above. The invention also relates to a head-up display comprising an image generating device as defined above.

The head-up display comprises for example at least one reflecting mirror. In one aspect, the image generation device is held in a head-up display housing and the heat sink protrudes outside the head-up display housing. This further enhances the removal of heat generated by the light emitting diodes.

Other advantages and characteristics will appear on reading the description of the invention, as well as the appended drawings in which: FIG. 1 is a diagrammatic perspective view in cross-section of an embodiment of a device; according to the invention, - Figure 2 is a schematic cross-sectional view of a detail of the device according to the invention, Figure 3 is a schematic side view of an embodiment of the heat sink, Figure 4 is a schematic perspective view of the lower face of a base plate of a heat sink, - Figure 5 is a perspective view of an embodiment of a device according to the invention, Figure 6 is a schematic view of an image generating device and a head-up display according to the invention. In these figures, the identical elements bear the same reference numerals. An example of an embodiment will now be described with reference to the figures. The following achievements are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features of different embodiments may also be combined to provide other embodiments. Figure 1 shows a schematic view of a section of an image generation device 10 according to one embodiment of the invention. The image generation device 10 comprises a liquid crystal screen, here a liquid crystal screen 12 (LCD screen) for example with thin film transistors, and a backlighting device 14. The LCD screen 12 can be active or passive matrix. Thin-film transistor thin-film screen 12 is commonly referred to as a Thin-Film Transistor Liquid Crystal Display (TFTLCD), and allows the image to be formed by the image generation device 10. The screen 12 is for example connected by a sheet of conductors or a flexible circuit 13 to a control electronics. The function of the backlighting device 14 is to provide the screen 12 with the light necessary for forming the image. To do this, the backlighting device 14 comprises: a plurality of light-emitting diodes 16 (also called LEDs or LEDs for "Light Emitting Diodes" in English, and used in the rest of the description) emitting light beams; an optical 20 for shaping the light beams, - a light diffuser 22 receiving the shaped light beams. The device 14 further comprises a heat sink 18 comprising at least two parts, namely on the one hand, a base plate 50 flat on its lower face 54 and a strip 52 folded in "crenellated" form, flat portions 6o forming contact areas being fixed directly against the underside 54 base plate 50, for example by gluing or welding. To ensure a good heat exchange, a thermal paste having a good thermal coefficient is interposed between the base plate 50 and the strip 52. According to the other nonlimiting embodiment of the invention, the strip can also be held by crimping on the plate. In other embodiments, the contact zones 60 are not necessarily flat but may be rounded as for example shown in FIG.

The multi-ply strip 52 forms cooling fins 80. The slotted form of the strip allows the cooling fluid to move by natural convection movement along the fins 8o forming open channels. on the outside 82 or closed 84, these closed channels being of course open at both ends. By way of non-limiting example, for good heat conduction and / or heat exchange with the cooling fluid, the base plate 50 and / or the strip 52 are made of aluminum. The strap can be in one piece. It can also be made in several parts, for example each of the parts having the shape of an "L", one segment is secured to the base plate while the other form cooling fin. In the context of this invention, any form of strip is possible and is not limited to the examples described here. In the case of natural convection, the shape and orientation of the fins will be determined so as to favor this convection as well as possible. It will be the same in the context of forced convection. The upper face 55 of the base plate 50 carries a supply circuit 21 of the light sources 16. This supply circuit 21 may be a printed circuit also called PCB (Printed Circuit Board in English). The printed circuit used can be for example of the type FR4 (for Flame Resistant 4 in English) or IMS (for Insulated Metal Substrate in English). A thermal paste with a very good thermal coefficient is disposed between the supply circuit and the upper face 55 of the base plate. The heat sink 18 includes a base plate 50 having a radiator function and cooling fins 8o disposed on the opposite face 54 to the one carrying the printed circuit and oriented perpendicular to the base plate 50. 2 0 2 9 The LEDs 16 are for example power LEDs, in particular with a power greater than or equal to 3W and placed so as to emit light in the direction of the screen 12. The screen 12 is inclined by predefined angle, preferably between 00 and 40 ° so as to obtain a vertical virtual image in the context of using the image generating device in a head-up display. The shaping optics 20 comprises, for example, a lens array 25, allowing the collimation of the light coming from the LEDs 16 to limit the losses of light power if a portion of light is not directed towards the screen 12 Generally, the lens array comprises an LED lens 16, each lens 25 being disposed above each LED 16. The diffuser 22 allows the light to be homogenized so as to illuminate the screen 12 so as to illuminate the screen 12. homogeneous to allow the formation of an image of good quality, that is to say substantially uniform brightness. In addition, the diffuser 22 can hide the inside of the backlight device. Other optical elements may be further disposed between the diffuser 22 and the screen 12 such as crossed prism filters or polarization films. By using a two-part heat sink according to the invention, the heat produced by the diodes 16 is more efficiently discharged so that the shaping optics can be placed closer to the LEDs. 16. In practice, the distance d between the lower face 70 of the lens 25 and the LED 16 can be reduced to a value between 0.3 and 07 mm, typically about 0.5 mm (see Figure 2). This also has the consequence that the height and size of the backlighting device can be reduced, which translates into a smaller footprint of a head-up display (HUD) as a whole, especially at light output. equal to the backlight device 10. This last point is very important in the space under the dashboard where the head-up display will be integrated and where every millimeter of won is very important. In addition, the optical efficiency of the device can be increased by placing the optical shaping optics closer, since the lateral losses of the light beam cone emitted by the LEDs 16 are reduced.

In order for the light propagating from the LEDs 16 to the screen 12 to remain in the backlighting device 14, the space contained between the LEDs 16 and the screen 12 is surrounded by a box 28, generally called a box. especially in the automotive field. To avoid losses of light power in the housing 28 by light absorption, it is made of a reflective material based on polycarbonate (abbreviated PC). For optimal reflection of the light, the housing 28 must have a very flat polished surface. According to a variant not shown, it can further cover the printed circuit of a reflective film with the exception of the location of LEDs 16. This reflective film may be a film made of polycarbonate (PC) having a higher reflection coefficient at 90%, preferably greater than or equal to 98%. Other materials can be envisaged for the reflective film, provided that they are adapted to the other constraints of the device 10.

In a variant, as can be seen in FIGS. 3 and 4, the base plate 50 of the heat sink 18 comprises, for example, on its face 54 grooves 56 of curved cross-section, in the form of a channel, and the cooling fins 80 are formed in the form of a channel. of a folded strip, the fold returns 58 being housed by being fixed in the grooves 56. In a variant, these grooves may be flat to receive a crenellated strip 52 such as 3 3 described previously. . Compared with cast aluminum, the thermal conductivity of unmolded aluminum is almost double. With this embodiment, the equivalent size heat dissipation is significantly improved. In a variant, this makes it possible to reduce the size of the heat sink and therefore of the backlight device as a whole. This better heat dissipation makes it possible to have a lower temperature at the level of light-emitting diodes and also increases the lifetime of these. The curved groove portion makes it possible to increase the contact area with the folds of the strip and therefore also a better heat dissipation. Figure 5 shows an alternative embodiment of the device according to the invention in which the base plate 50 is folded in a bend or fold 94 so that the bottom face 54 of the base plate has two planes of different orientations. For example, a first plane 92 is located right of the housing 28 which contains the printed circuit 21 and the leds 16 to be cooled. The lower face 54 of the base plate 50 in this case does not carry a cooling strip 20 at this plane 92. This situation can arise for example when no space is available to place the strip of cooling. Another reason is that it is desired to arrange the strip in a different orientation which will, for example, provide better natural convection by orienting the fins 80 so that the hot air can move easily upward with the minimum constraints. Thus, in the embodiment of Figure 5, the strip is placed on a lower face 54 of the base plate 50 oriented in a plane 98 different from the plane 92 described above. With respect to the housing 28 and in particular with respect to the location of the LEDs 16, the base plate 50 is extended so as to form a cantilever on which the strip is arranged, this overhang being here oriented in a plane different from that carrying the housing 28. A hole 86 allows the passage of a screw for fixing the strip. Alternatively, for example for reasons of space, the base plate 50 may have a simple overhang, that is to say without fold 94 of the base plate 50. In this case, the two previously described plans 92 and 98 are merged. As illustrated in FIG. 6, the invention also relates to a head-up display 200 comprising an image generation device 10 according to the invention. The image generation device 10 described with reference to FIG. 1 forms an image using the liquid crystal screen 12. Downstream of the screen 12 according to the direction of movement of the light beam, 15 display 200 comprises at least one semi-reflecting plate 126 and a reflection device 125 interposed in the path of the image between the screen 12 and the semi-reflecting plate 126, the reflection device 125 comprising one or more plane mirrors or As shown in FIG. 6, the path of the image is symbolized by three dotted arrows 30 which reflect on the reflection device 125 before being displayed through the semi-reflective plate 126. This latter allows a magnification and / or, by transparency, a display of the image beyond the semireflective blade, in particular beyond the windshield of the equipped vehicle, at a virtual screen 130, obtained at ugly e of the semi-reflecting blade 126. 25 This blade 126 has a reflection power of at least 20%, which allows the user to see through the blade the road taken by the vehicle, while benefiting from the a high contrast to see the image displayed. Alternatively, the display of the image can take place at the level of the windshield of the vehicle equipped with said display 200.

As shown in FIG. 6, the image generation device 10 is held in a head-up display unit 210 and the heat sink 18 of the backlight device 10 projects outside the display box 210. head, which further improves the evacuation of the heat produced by the light-emitting diodes 16. A transparent hatch 132 of concave shape is formed in the housing 210 to allow the light beam reflected by the reflection device 125 out of the housing 210 .

The use of the heat sink 18 constituted on the one hand by a base plate 50 and a strip 52 makes it possible to better evacuate the heat so that the lenses 25 can be placed closer to the LEDs 16. the image generator is reduced. Thus a gain of a few millimeters over the distance di between the screen 12 and the heat sink 18 may result in a space saving of a few centimeters over the distance d2 between the image generator 10 at the bottom of the housing 210 of the head-up display 200 (HUD) thanks to the amplification or magnification effects of the various mirrors placed in the housing 210 of the head-up display 200.

Claims (10)

REVENDICATIONS1. Backlighting device (14), in particular for a head-up display comprising: - at least one light-emitting diode (16) emitting light beams, an optics (20) for shaping the light beams, - a diffuser (22) light receiving the shaped light beams characterized in that it further comprises a heat sink (18) made of at least two parts comprising on the one hand, a base plate (50) and on the other hand at least a strip (52) fixed on said base plate, the strip comprising at least one fold (go) to form at least one cooling fin (8o) and at least one zone (60) intended to come into thermal contact with said plate basic (50). 2. Device according to claim 1, characterized in that the strip (52) comprises several folds (go) and several areas (60) in contact with the base plate (50). 3. Device according to the preceding claim characterized in that the strip has a crenellated form. 4. Device according to any one of the preceding claims characterized in that a thermal paste, is interposed between the base plate (50) and at least one contact area (6o). 5. Device according to any one of the preceding claims characterized in that the strip is fixed on the base plate (50) by welding, screwing or crimping. 6. Device according to any one of the preceding claims characterized in that the strip (52) and / or the base plate (50) are aluminum. 7. Device according to any one of the preceding claims, characterized in that the strip (52) is disposed on a lower face (54) of the base plate (50) opposite an upper face (55) of the plate of base carrying the light-emitting diodes (16). 8. Device according to any one of the preceding claims, characterized in that the base plate (50) of the heat sink (18) has on its side opposite to that carrying the light emitting diodes (16) grooves (56) housing the fins (80). 9. Device according to the preceding claim, characterized in that the grooves have a curved or flat cross section and in that the contact areas (60) of the cooling fins (80) are made in the form of a folded strip, the fold returns accommodating by being fixed in grooves (56) of curved or flat cross section. 10. Device according to any one of the preceding claims characterized in that the strip (52) is in line with the light emitting diodes (16). he. Device according to any one of claims 1 to 9 characterized in that the strip (52) is offset with respect to the location of the light-emitting diodes (16) and arranged on an extension (98) of the base plate (50) . 12. Device according to the preceding claim, characterized in that the extension (98) of the base plate (50) has a differentdifferente of the portion of the base plate located at the right of the light emitting diodes (16). 13. Device according to the preceding claim, characterized in that the base plate (50) comprises a fold (94) so that extension (98) of the base plate (50) may have a different orientation of the plate portion this base located at the right of the light emitting diodes (16). 14. Device according to any one of claims 1 to 13, characterized in that the optics (20) shaping comprises a lens array (25), each lens (25) being placed in front of a diode electroluminescent (16) and forming collimator. 15. An image generating device (10), in particular for head-up display, comprising a liquid crystal screen (12) and a backlighting device (14) of this liquid crystal screen (12) according to one Any one of claims 1 to 14. A head-up display (200) comprising an image-generating device (10) according to claim 15. A head-up display (200) according to claim 16, characterized in that it comprises at least one reflecting mirror (125). A head-up display (200) according to claim 16 or 17, characterized in that the image generating device (10) is held in a head-up display housing (210) and the heat sink ( 18) protrudes outside the head-up display housing (210).